Excellent article by Peter Lemme. It describes the stall characteristics of airliners, and the certifacation rules that apply.
Apparently the MAX is unstable aircraft without MCAS. It is not unstable as modern fighters are, but one can argue that stall characteristics of the MAX renders it un certifiable according to FAR 25 certification standards, but with MCAS working it meets the criteria.
So how is it possible to certify the MAX and not having to demonstrate stall behaviour with MCAS off?
Yes, the article is an interesting qualitative discussion of stall characteristics. I still don't quite understand the reason for the "stick lightening," though. The usual answer so far has been that the nacelle generates lift at a sufficiently high angle of attack, and that lift generates the extra pitching moment that the pilot does not have to generate through the stick (hence, stick lightening).
However, the nacelle is an annular airfoil, and annular airfoils tend to stall relatively late, so the CL(alpha) relationship is basically linear through the stall angle of the isolated wing and beyond (depending on the internal "airfoil like" shape of the nacelle). In other words, if this applies to the MAX as well, the nacelle lift would decrease the slope of the Cm(alpha) curve, but by the same amount for all alphas through stall and beyond, and would not cause the change in slope that we call "stick lightening".
If the NG complies with FAA regulations about the linearity of the force-alpha curve, and if (repeat, if) the nacelle has a linear behavior too, then it might be something related to something new introduced by the coupling of the engine and the wing, such as different patterns of flow separation induced by having this big engine basically in front of the leading edge of the wing. Identifying true reason for the stick lightening might be academic, but it might also have an impact of what MCAS is supposed to do.
There was a discussion on this general area in the Tecnical forum a few months ago, but it stopped before it got to this point.